1. Field of the Invention
The present invention relates to an optical device having an optical system mount plate, on which an optical system is mounted, and a casing, in which the optical system mount plate is housed, and more particularly to an optical device in which a bottom of the casing is provided with a screw-hole forming part which is threadingly fit on a screw provided on a tripod head.
2. Description of the Related Art
As examples of optical devices, there are a binocular telescope, a camera, and so on. In these optical devices, an optical system mount plate is housed in the casing, and an optical system, such as an observation optical system and a camera, is mounted on the optical system mount plate. The optical device is usually designed to be fixed on a tripod head. Namely, a screw-hole forming part is provided on a bottom of the casing, and is threadingly fit on a screw of the tripod head, so that the optical device is attached on the tripod.
On the other hand, the optical device is required to be light weight. Therefore, aluminum, aluminum alloy, and reinforced plastic are used as material for the casing, and the thickness of the casing is required to be as thin as possible. Usually, the screw-hole forming part is integrally formed on the bottom of the casing, and has a large thickness so as to form a screw hole.
When the optical device is attached to the tripod head, it is often the case that excessive rotational force is exerted on the screw-hole forming part by tightening the screw of the tripod head to the screw-hole forming part. Due to this excessive rotational force, excessive stress occurs in the bottom of the casing, so that the casing may be deformed.
Thus, for lightening the weight of the optical device as a whole, it is desirable to reduce the thickness of the casing. However, for preventing deformation of the casing from occurring, because of the excessive stress when attaching the optical device onto the tripod head, it is not possible to reduce the thickness of the casing too much.